Dual-Atom Metal and Nonmetal Site Catalyst on a Single Nickel Atom Supported on a Hybridized BCN Nanosheet for Electrochemical CO 2 Reduction to Methane: Combining High Activity and Selectivity.

Atomically dispersed nitrogen-coordinated transition-metal sites supported on graphene (TM-N 4 -C) offer promising potential for the electrochemical carbon dioxide reduction reaction (CO 2 RR). However, a few TM-N x -C single-atom catalysts (SAC) are capable of reducing CO 2 to multielectron products with high activity and selectivity. Herein, using density functional theory calculations, we investigated the electrocatalytic performance of a single TM atom embedded into a defective BCN nanosheet for CO 2 RR. The N and B atom co-coordinated TM center, namely, TM-B 2 N 2 , constructs a symmetry-breaking site, which strengthens the overlapping of atomic orbitals, and enables the linear CO 2 to be curved and activated, compared to the weak coupling of CO 2 with the symmetric TM-N 4 site. Moreover, the TM-B 2 N 2 sites play a role of dual-atom active sites, in which the TM atom serves as the carbon adsorption site and the B atom acts as the oxygen adsorption site, largely stabilizing the key intermediates, especially *COOH. The symmetry-breaking coordination structures shift the d-band center of the TM atom toward the Fermi level and thus facilitate CO 2 reduction to hydrocarbons and oxygenates. As a result, different from the TM-N 4 -C structure that leads to CO as the major product, the Ni atom supported on BCN can selectively catalyze CO 2 conversion into CH 4 , with an ultralow limiting potential of -0.07 V, while suppressing the hydrogen evolution reaction. Our finding suggests that introduction of a nonmetal active site adjacent to the metal site provides a new avenue for achieving efficient multi-intermediate electrocatalytic reactions.